Maintenance of an upright bipedal postural stance and the recover of balance following a perturbation depends on the integration of sensory input from the somatosensory system, the visual system and the vestibular organs. The relative contributions of these three sensory systems to the maintenance of postural stance and to the balance recovery are not well understood. Least is known about the role of the different components of the somatosensory system, in part because of the inherent difficulty of manipulating the individual proprioceptors (cutaneous, joint receptors, golgi tendon organs, and muscle spindles) that make up this system. In preliminary experiments, we have demonstrated that the somatosensory system is at least as important as vision in the maintenance of upright stance and that the compensation of one sensory system for another is far from complete. In this proposal, we outline experiments that further isolate the relative contributions of the different components of the somatasensory input during upright bipedal stance and during recovery of stance following a perturbation of the support surface. This goal will be achieved by exploiting the unique model of diabetic peripheral neuropathy and the careful seletion of subjects based upon relative deficits in their perception of ankle joint movement and the loss in plantar cutaneous sensation. The first aim is to fully characterize the specific loss of cutaneous sensation and perception of ankle joint movement in diabetic patients with peripheral neuropathy. The relative severity of these losses is not well known due to a lack of focus in the past on the effects of diabetic polyneuropathy on the proprioceptive receptor pathways. Psychophysical touch and movement perception thresholds will be used to reveal the status of plantar cutaneous receptors and ankle proprioceptors in a large group of diabetic patients at various stages in the course of diabetic peripheral neuropathy.